Heat exchangers including a serpentine flat tube and corrugated fins disposed between parallel sections of the tube used in an air conditioning system are well known. In brazing the serpentine tube and corrugated fins, various methods for coating flux have been employed. For example, a slurry of flux may be sprayed onto the heat exchanger, or the heat exchanger can be dipped into a flux bath, or electrostatic powdered flux may be blown onto the heat exchanger. The electrostatic powder is a dry powder, thus water is not used in blowing or coating the heat exchanger. It is not necessary to use a drying process when blowing an electrostatic powdered flux. On the other hand, it is necessary to use a drying process when spraying a slurried flux or when the heat exchanger is dipped in a flux bath. The coat of flux is relatively even, but despite cost savings over manually applying the flux, these methods suffer from disadvantages.
The brazing method using the above method of blowing a powdered electrostatic flux is explained as follows. A heat exchanger is temporarily assembled by disposing corrugated fins between the parallel flat outer surfaces of a serpentine flat tube which is fixed in position by a jig. The temporarily assembled heat exchanger is charged with electricity in reverse polarity to the flux. The powdered electrostatic flux is then blown onto one side surface of the heat exchanger. The powdered electrostatic flux attaches to the sides of the heat exchanger by an attractive electrical force. Thereafter, the heat exchanger is heated in a furnace, which completes the brazing process.
However, since the flux coats or attaches to the surface of the heat exchanger by only an attractive electrical force, this gives rise to a poorly coated heat exchanger. In addition, since the flux is blown onto only one side of the heat exchanger, the amount of flux which attaches to the other side of the heat exchanger is considerably less. Thus, a lack of uniformity in attaching the flux exists.
Alternatively, and as a means for solving the above problems, it has been suggested that two machines be employed for blowing the flux on both sides of the heat exchanger. If two machines are used in this way, then the cost of the fluxing method significantly increases. Also, the amount of flux that attaches to the heat exchanger does not increase as the amount of flux being blown onto the heat exchanger increases. However, some of the excess flux will be carried into the furnace. The excess flux is waste which causes the interior of the furnace to be fouled.